A woman in her 80s is in a serious condition in hospital after an accident involving a police motorbike escorting the Duke and Duchess of Cambridge.

William and Kate were on their way to a ceremony in Windsor on Monday when a marked police motorbike in their convoy was involved in a collision with the woman on Upper Richmond Road, Richmond, south-west London.

The woman, named locally as Irene Mayor, was taken to hospital in a critical condition, Scotland Yard said.

The duke and duchess are “deeply concerned and saddened” by what happened, Kensington Palace said. They are understood to have sent flowers.

The Independent Office for Police Conduct (IOPC) is investigating the circumstances of the collision which involved a motorcycle attached to the Royalty and Specialist Protection Command.

A witness told The Sun: “His bike hit her and she spun round, off her feet and fell badly on the floor.”

Her daughter Fiona told the newspaper the royal couple have offered to visit.

She added: “She’s got lots of injuries. They are just keeping her stable at the moment.”

Another witness, who did not want to give his name, told the Press Association he saw a woman lying in the road in the aftermath of the accident when he opened one of his windows.

The 76-year-old said: “There were people around her trying to make her comfortable – bringing blankets and putting a pillow under her head, that kind of thing.

“Everyone was talking to her so she was awake. I don’t think her legs were moving at all but her arms were moving slightly.

“I saw a police bike… and it was on its side, on the wrong side of the road facing the wrong way.”

An IOPC spokesman said: “The woman, in her 80s, suffered serious injuries and was taken to a London hospital where she remains in a serious but stable condition.

“In line with procedure, the Metropolitan Police Service referred the collision to the IOPC.

“Our staff attended the scene of the incident and after careful consideration, we have launched an independent investigation.

St George's Chapel
William and Kate had been on their way to St George’s Chapel for the annual Order of the Garter Service at Windsor Castle (Ben Stansall/PA)

“The investigation is in its very early stages and the officer involved is assisting our inquiries as a witness.

“Our immediate thoughts are with the injured woman and her family and those affected by the incident.”

Kensington Palace said: “The Duke and Duchess of Cambridge were deeply concerned and saddened to hear about the accident on Monday afternoon.

“Their Royal Highnesses have sent their very best wishes to Irene and her family and will stay in touch throughout every stage of her recovery.”

The accident took place at around 12.50pm on Monday when the royal couple were on their way to Windsor for the St George’s Chapel service commemorating the Order of the Garter.

Giles Oakley, a neighbour who lives opposite Ms Mayor, told the Press Association: “They’re a lovely family.

“It is very, very sad that Irene has been injured. She is a very sweet person and is very well liked in the street.”

Earlier this year, the Duke of Edinburgh, 98, surrendered his driving licence after a crash at Sandringham.

Philip flipped his Land Rover Freelander on January 17 after colliding with a Kia as he pulled out onto the A149 in Norfolk.